The present invention belongs to the field of high-fidelity electronic audio technology and more particularly pertains to a current analog audio amplifier.
Conventional amplifiers adopt negative feedback technology in the hope of achieving low distortion and ultra-wide frequency response. Unfortunately, although the negative feedback technology can reduce the distortion of general amplifiers and broaden the frequency response, transient intermodulation distortion caused by conventional negative feedback audio amplifiers when processing large dynamic high frequency signals produces “dry” and unpleasant sound, and gradually becomes system bottleneck. In order to avoid transient intermodulation distortion, technologies with shallow negative feedback and even without feedback should be used. These technologies pay a high price, yet none of them can fundamentally solve the problem. System stability problems may also exist. Machines or even speakers are easy to be burned due to electrical fault.
Since phase shift problems exist in conventional negative feedback circuits, distortion of conventional audio amplifiers at high frequencies (6 kHz above) is obviously worsened in comparison with that at 1 kHz. Full-range ultra-low distortion is not possible.
Currently, high resolution mastering music is popular. Audio band extends to 100 kHz. The dynamic range reaches up to 120 dB. Conventional voltage-analog audio amplifiers cannot achieve ultra-wide frequency response due to limitations of circuit structure. People's demand for a new high-fidelity power amplifier with wideband and low distortion is more urgent.
In 1975, Gilbertc invented the word “translinear” which was first reported at the ISSCC, marking that the current analog concept was formally introduced. At the 87th AES Society Convention in 1989, British scholar D. C Wadsworth first proposed that the application of current analog circuits in audio can result in an ultra-fast and ultra-low distortion technical performance. In 2005, Wang Fengshuo (the applicant himself) applied a utility model patent for “Current Analog High Fidelity Power Amplifier” based on full discrete devices. However, since the amplifier performance depends on the matching and screening of the discrete devices, translinear (TL) circuit inside the current analog amplifier has strict requirements in matching transistors. Problems of consistency of product performance as well as higher actual production cost exist. In a current analog circuit, the transistor interelectrode capacitor which affects the speed and bandwidth works on very low impedance nodes (usually a few ohms to dozens of ohms only, which is one hundredth to one thousandth of the impedance nodes for a general voltage analog amplifier). Under the effect of the current signal having a large swing, charging and discharging of the transistor interelectrode capacitor can be done quickly, so the working speed under large signal is much quicker than conventional voltage analog circuit. Influence of parasitic capacitor in the circuit on distortion is also avoided. Thus the current analog circuits are with ultra-high precision and ultra-low distortion.